Method and apparatus utilizing a magnetic armature and sensing coil for determining flatness



Dec. 15, 1964 H. E. BRYs 3,161,824

METHOD AND APPARATUS UTILIZING A MAGNETIC ARMATURE AND SENSING COIL FOR DETERMINING FLATNESS Filed June 25, 1958 2 Sheets-Sheet l www IQOOI,

INVENTOR.

ATTORNEYS.

Dec. l5, 1964 H. E. BRYs 3,161,824

METHOD AND APPARATUS UTILIZING A MAGNETIC ARMATURE AND sENsING con. FOR DETERMINING FLATNEss ATT'cRNEYS.

United States Patent Oiiice 3,16 1,824 Patented Bec. 15, 1964 3,161,824 ME'IHD AND APPARATUS UTILIZING A MAG- NETIC ARRJATURE AND SENSING CGIL FR BETERMINING ELATNESS Harry Engene Erys, Butter, Pa., assigner to armee Steel Corporation, Middletown, Ghia, a corporation o hio Filed ,lune 23, Igd, Ser. No. 743,633 4 Cima. (Ci.1 324-34) This invention relates .to a flatness gauge and more particularly to an apparatus for the purpose of measuring the deviation of a body from a `standard or arbitrary degree of flatness, and is a continuation-impart of my copending application, Serial No. 553,542 tiled December 16, 1955, now abandoned. The body may be a sheet, strip, block or the like and in the operation of the apparatus I make use of the quali-ty of magnetic permeability. The apparatus according to the invention is particularly Well adapted to the gauging of fiatness of metallic strip having some degree of magnetic permeabiiity and it is adaptable to measuring the flatness of so-called non-magnetic materials such as stainless steels and alloys which are generally thought to be non-magnetic but which do possess some degree of permeability Which can be employed according to the present invention.

The invention is `also adaptable to the measurement of the latness of materials which possess slight or air permeability. I shall hereinafter disclose a modification wherein for use with materials which actually have air permeability I provide an armature adapted to` rest on the material being gauged but in this modification the thickness of the material being gauged will be limited to the flux iield of the sensing element and a workable deviation of the armature.

All tlatness gauges which have been proposed in the past, and with which I am familiar, have various n1echanical parts which are exposed to damage and thus errors and miscalibrations can enter into the readings by accident. Generally such apparatuses involve the direct mechanical displacement of a magnetic core or armature and in addition to the unreliability of such apparatuses, they involve excessive maintenance costs.

It is an object of the present invention to provide an apparatus to measure atness or deviation from a set or standard degree of flatness, wherein it is possible in most cases to measure flatness Without actually contacting the body whose atness is to be measured and wherein no damage can accrue to the sensing elements. It is another object of the invention to provide a device of .the character outlined which will be dependable and maintenance-free in operation and which does not involve mechanical wear. Still another object involves the provision of an apparatus wherein a true zero or base line is established and wherein there will be no drift in calibration.

These and other objects of the invention which will be described in greater detail hereinafter or which will be apparent to one skilled in the art upon reading these speciications, I accomplish by that certain construction and arrangement of parts of which I shall now disclose certain exemplary embodiments.

Reference is made to the drawings forming a part hereof and in which:

FIGURE l is a diagram illustrating the invention.

FIGURE la is a side elevational view of the testing table.

FIGURE 2 is a fragmentary cross-sectional view through the testing table taken on the line 2-2 of FIG- URE la on an enlarged scale.

FIGURE 3 is a fragmentary View similar to FIGURE l but showing a modiiication.

FIGURE 4 is a view similar to FIGURE 2 but showing a modification.

FIGURE 5 is a fragment-ary cross-sectional View taken on the line 5 5 of FIGURE 4 and on an enlarged scale.

FIGURE 6 is a fragmentary cross-sectional View taken on the line 6-6 of FIGURE 4, also on an enlarged scale.

FIGURE 7 is an elevational view of the yoke member seen in FIGURES 5 and 6.

FIGURE 8 is a bottom plan view of FIGURE 7; and

FIGURE 9 is a graph useful in understanding the principles of the invention.

Briefly, in the practice of my invention, I provide a table over which the material to be tested may pass. The material may be gauged while it is stationary or it may be gauged While in motion. The sensing element or elements are in the `form of wound coils and are recessed in suitable recesses in the table. The recesses are covered with a plate of any suitable material having substantially air permeability to maintain the at surface of the table.

In the practice of my invention, I may use coils having an -air core or cciis having an iron core. Certain considerations, which will be described more in detail hereinafter, must be observed when the coils are provided with an iron core.

Referring in more detail to the drawings, and more particularly to the embodiment of FIGURES 1 to 3 ininclusive, the table is indicated generally at 1G and a strip Whose ilatness is to be gauged is indicated at 11. The coils which constitute the sensing element are indicated at 12 and they are suitably mounted in recesses 13 in the table 10. The recesses 13 are covered by the plate 14 of any suitable material having substantially air permeability. It will be clear that any desired number of such sensing elements may be employed, depending upon the Width of the material to be gauged. I have shown in these drawings a single row of sensing elements, three in number, extending transversely of the strip to be gauged.

The sensing element 12 consists of coils of air cores and their purpose is to measure the proximity of various areas of the strip 11 without magnetically attracting the strip or drawing it toward the gauging elements.

The numeral 15 indicates a balanced bridge circuit which includes a voltage regulating transformer 16, two condensers 17 and 18, a full wave rectifier, 19 and a ltering or damping condenser 2t?.

A series of coils 25 substantially identical to the coils 12 and equal in number to the number of coils 12, are disposed in alternate recesses in the table l@ so that there is a coil 25 adjacent each coil 12. The coils 25 are compensating coils and their purpose is to neutralize the signal respectively of the coils 12 when no strip is on the table to be tested. The coils 25 are suitably rendered unaffectable by the strip to be tested as by shielding, by being placed at a greater distance, by being placed on a horizontal axis, or in some other Well known manner. (Not shown.) Thus, when no` strip 1l is on the table 10 to be tested and the machine is energized, the coils 25 respectively neutralize the signals from the coils 12 so that a signal resulting from the coils 12 when a strip is being tested is produced only by the presence of the strip. With this arrangement, temperature compensation is inherent -because the coils 12 and 25 are physically located beside each other so that they are affected by the same temperature to the same degree.

The coils 12 and 25 are inductively and resistively balanced, so that an unbalance resulting from displacement of a body having magnetic permeability with respect to the coil 12, will result in an output from the balanced bridge circuit.

it will be understood that each sensing element may armena have a separate indicating or recording channel or the total or average may be algebraically computed by suitable equipment which does not form a part of the present invention. The output of the bridge circuit may feed a suitable indicating device such as a meter for direct viewing without recording. Of course, the output from the bridge circuit may be connected to a recording instrument but this may require ampliiication by means of magnetic or electronic amplifying devices. lt will also be understood that the output of the bridge circuit may be used to apply corrective measures or to perform other desirable functions such as classification, rejection or signalling by means of devices in the public domain. In FIGURE l, l have diagrammatically shown the output of the bridge circuit as being amplified and feeding an oscillograph. The oscillograph shows six traces. Three of these correspond to readings from the three coils i2, each of which will have a circuit such as that of FIG- URE l. The remaining three traces may be arranged in known manner to record strip speed, strip gauge and strip tension. lt will be found of value in many instances to correlate speed, distance and gauge with liatness at the two edges of the strip and the middle.

The bridge circuit is balanced when there is no permeable material on any sensing element. The zero line of the indicating or recording mechanism representing perfect flatncss (or maximum unbalance of the bridge circuit) is attained when the material being gauged is as close as possible to the sensing element. If now the material being gauged deviates from its nearest proximity to the sensing element, the electrical bridge will be moved toward balance and the recording or indicating instrument will be moved away from its zero. The movement away from zero of the instrument is proportional to the deviation of the material being gauged. It will be understood that the circuitry is calibrated in order to obtain desired readings in relation to the mechanical deviation expected. ment may be calibrated to read in any desired terms such as percentage, millimeters, one-thousandths of an inch, etc.

Since the operation of the device is based upon rnechanical deviation from a sensing coil of a material having some magnetic permeability, it will be clear that modification must be made if it is desired to measure the fiatness of material having air permeability or extremely low permeability. Such a modification is shown in FiG- URE 3, where an armature 35, which may be in the form of a wheel or which may be supported on wheels, is mounted by means of an arm 26 from a bracket 2'7 so as to ride freely on the material to be gauged. In this instance, the sensing element senses the proximity of the yarmature which reflects the deviation of the air permeability material. The armature 35 may of course be adjusted as to pressure or weight in a known manner. @ne such adjustment is shown in FIGURE 3 where the arm 26 is mounted to the bracket 27 by a ball bearing pivot at 25d and is threaded at 26a. A counterweight 26h is threaded onto the arm 26 so that by turning the counterweight 26h it may be moved along the arm 26. When properly adjusted, its position is fixed bymeans of a jam nut 2de. It will be understood that in the modification of FIGURE 3 I am limited as to thickness of material to be gauged by the flux field of the sensing element 12 and the workable deviation of the armature 35.

Again in the modification of FGURE 3, there is no electrical sensing element exposed to mechanical damage. The armature 35 is easily replaceable in the event of damage and is an inexpensive element.

In the modification of FIGURES 4 to 8 inclusive, l have shown the use of coils having iron cores. The structure of the table may again be substantially as described above, at least t the extent that means are provided beneath the table for the mounting of the sensing coils and the compensating coils and that these coils The indicator or the recording instruiare covered with a material having no permeability to provide a smooth iiush surface for the passage of the strip lli to be tested. In FGURES 4, 5 and 6 the table is indicated at Titia.

With coils having metallic cores care must be taken that the signals of the sensing coils are: completely neutralized just as with coils having air cores. It is desirable particularly in the testing of material having oriented grain structure to concentrate the liux field in the direction of grain orientation. For this purpose the sensing coils i251 havin the iron cores i2!) are provided with the iron yokes Mc. These serve the function ot concentrating the lines of force in the direction of grain orientation of the strip being tested. This is a standard E yoke. lt will be observed that in FIGURE 5 the sensing coil is shown mounted with the open side of the yoke llic upwardly. The compensating coil 25a shown in FlGURE 6 is in all respects like the sensing coil F.2d except that it will be observed that it is mounted in inverted relation and with the open side of the yoke l2@ extending downwardly. llZd indicates a strap by means of which the coil, whether it be 12a or 25a, may ce mounted. Parts of the coil are riveted together as shown, and the assembled coils are clamped between the upper plate lid-b and lower plate 14C by the bolts Kili.

By mounting the compensating coils 25a in inverted position in relation to the coils 12a, they neutralize each others signal so that when no strip is being tested no signal is derived from the coils 12a and when a strip is being tested the signal derived from the coils 12a is produced only by the spacing between the strip and the coils Ilia.

ln FlGURE 9, I have shown a graph for a typical installation on which A.C. voltage is plotted against distance in inches from the -coil llZa and it will be noted that from a little over one-sixteenth inch up to approximately one-half inch the curve is a straight line. Particularly when working with coils having iron cores, it is important to operate in the flat or linear part of the curve so that the readings in terms of deviations from the flat will be linear, While the distance may be as great as one-half inch, it is preferred that it not exceed threeeighths inch and preferably that it not be less than onesixteenth inch. An ideal spacing is about one-fourth inch and excellent results can be obtained with this spacing.

lt will be understood that the details of the amplifier and the recording or indicating instrument do not constitute a part of the present invention and it is to be understood that in the claims when indicating means are referred to, such means are inclusive of recording means.

It will also be clear that numerous minor modifications may be made Without departing from the spirit of the invention and l, therefore, do not intend to limit myself otherwise than as indicated in the claims which follow.

Having now fully described my invention, what l. claim as new and desire to secure by Letters Patent is:

1. An apparatus for determining the deviation from an arbitrary degree of fiatness of a body having substantially air permeability, comprising a table upon which a body to be examined is located, said table having a recess, a sensing coil disposed in `said recess, a plate of a material having substantially air permeability covering said recess and flush-mounted in said table to provide a continuous smooth surface, a second coil, said coils being inductively and resistively balanced, a balanced bridge circuit including said coils, said sensing coil being disposed at such distance from the body to be examined that the A.C. response is linearly related to the proximity vto said sensing coil of an element of said body under examination, an armature having magnetic permeability disposed to rest lightly on said body over said sensing coil and to be displaced by elevations or depressions in said body to affect the liux eld of said sensing coil to unbalance said bridge circuit proportionately to the proximity of said armature to said sensing coil, said bridge circuit having an output, and indicating means connected to said output to indicate the degree of said nnbalance and therefore the degree of atness of said body.

2. An apparatus according to claim 1, wherein said armature comprises a Wheel and means to counterbalance the weight of said armature,

3. An apparatus according to claim 1, wherein said body is a strip of material and wherein a plurality of sensing coils are disposed in a row transversely of the strip, each sensing coil having the associated elements of claim 11.

4. The method of measuring the deviation of a metallic strip having substantial air permeability from an arbitrary standard of atness, which comprises providing an inductive sensing device having a neutral response when no metallic strip is in proximity thereto, passing said strip, free from flattening influence thereon, over said sensing device, causing a body having magnetic permeability to ride on said strip over said sensing device without substantially affecting the flatness of said strip, to cause said sensing device to respond to the inductance generated therein by said body, the proximity being such that the inductance generated by said body at a given point is linearly related to the distance between said strip at said given point and said sensing device, and indicating the inductive response of said sensing device.

References Cited in the file of this patent UNTTED STATES PATENTS OTHER REFERENCES General Electric Review, pages 486, 487, Nov. 1939. 

4. THE METHOD OF MEASURING THE DEVIATION OF A METALLIC STRIP HAVING SUBSTANTIAL AIR PERMEABILITY FROM AN ARBITRARY STANDARD OF FLATNESS, WHICH COMPRISES PROVIDING AN INDUCTIVE SENSING DEVICE HAVING A NEUTRAL RESPONSE WHEN NO METALLIC STRIP IS IN PROXIMITY THERETO, PASSING SAID STRIP, FREE FROM FLATTENING INFLUENCE THEREON, OVER SAID SENSING DEVICE, CAUSING A BODY HAVING MAGNETIC PERMEABILITY TO RIDE ON SAID STRIP OVER SAID SENSING DEVICE WITHOUT SUBSTANTIALLY AFFECTING THE FLATNESS OF SAID STRIP, TO CAUSE SAID SENSING DEVICE TO RESPOND TO THE INDUCTANCE GENERATED THEREIN BY SAID BODY, THE PROXIMITY BEING SUCH THAT THE INDUCTANCE GENERATED BY SAID BODY AT A GIVEN POINT IS LINERALY RELATED TO THE DISTANCE BETWEEN SAID STRIP AT SAID GIVEN POINT AND SAID SENSING DEVICE, AND INDICATING THE INDUCTIVE RESPONSE OF SAID SENSING DEVICE. 